Organic acids (OAs) have been used as natural preservatives for food products and as hygiene promoters to inhibit microbial growth, thereby improving the freshness and shelf-life of food items. The impact of OAs on microbial growth makes it an alternative to antibiotic growth promoters. The characteristic of inhibiting microbial growth is a useful feature that has been recently used in poultry production. Organic acids are chemically weak, and they modulate the beneficial competitive exclusion in the gastrointestinal tract (GIT) and diminish the production of metabolites harmful to the body by decreasing the proliferation and colonization of pathogenic bacteria in the GIT. Further, they improve the ability of the intestinal wall to absorb nutrients by improving the structure of the villi and the digestive secretions that lead to enhanced absorption of proteins, carbohydrates, and minerals. The use of 15g/kg of citric acid in broiler diets reduced the cecal total bacterial count and Enterobacteriaceae by 62.26% and 80%, respectively, in comparison with control. However, the same level of fumaric acid reduced the cecal total bacterial count and Enterobacteriaceae by 88.63 and 78.57%, respectively. Similarly, the inclusion of 30g/kg of fumaric acid reduced the cecal total bacterial count and Enterobacteriaceae by 95.84 and 88.57%, respectively. The immunity of broilers can thus be improved as a normal consequence of all previously mentioned advantages. The use of 0.30 g/kg blends of sorbic acid, fumaric acid, and thymol improved the spleen size of broiler chickens by 50% when compared to control. Dietary inclusion of formic acid up to 5 and 10 g/kg significantly improved feed conversion ratio by 9.37 and 16.66% and improved ileal digestibility of crude protein by 19.85 and 21.08%, respectively. This chapter summarizes the possible modes of action of dietary OAs and their effects on the growth and health of poultry.